Saxon

In a user defined function which has a tail recursive call, we observe When bytecode generation is on, the exception java.lang.NullPointerException is thrown. This occurs when the tail call is within a singleton for-loop which at runtime may be ran zero or one time.

The exception can be reproduced with the following function (taken from http://dnovatchev.wordpress.com/):

<xsl:function name="my:processQueue"  as="xs:string*">
  <xsl:param name="pQueue" as="element()*"/>
  <xsl:param name="pTarget" as="xs:string"/>
  <xsl:param name="pExcluded" as="xs:string*"/>
  
  <xsl:sequence select=
   "if(not($pQueue))
      then ()
      else for $vTop in $pQueue[1],
               $vResult in my:processNode($vTop, $pTarget, $pExcluded)[1]
		         return
		           if($vResult/self::result)
					       then string-join($vResult/*, ' ==> ')
					       else my:processQueue((subsequence($pQueue, 2), $vResult/*),
					                            $pTarget,
					                            ($pExcluded, $vResult/*/value)
					                           )"/>
 </xsl:function>